Fatigue crack propagation of sheet molding compounds in various evironments

The effect of the absorption of water and isooctane on the rate of fatigue crack propagation of sheet molding compounds (SMC‐R30 and SMC‐R65) was investigated. A crack extension gage was used to measure the crack length. Results show that the absorption of water decreases the rate of fatigue crack propagation in the initial cycles but increases the rate of propagation in the final cycle. The absorption of isooctane into SMC‐R65 tends to decrease the rate of fatigue crack propagation. Microscopic observation shows considerable swelling of the polyester matrix due to the absorption of water and no significant apparent effect due to the absorption of isooctane.